Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds genuinely useful context beyond that: only show_in_rest-registered meta is visible (so absence of a key is not proof it doesn't exist), plus the operational note that the server marks it read-only so it executes without approval. It does not cover what happens for an unregistered key or error behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Four tight sentences, front-loaded with what is returned and its visibility constraint, then parameters, then execution behavior. The "Through Royally" clause is slightly awkward filler but carries a real detail (auto-execution) so it still earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

No output schema exists, and the description compensates by describing both return modes (all meta vs. single-key object) and the show_in_rest visibility limit. Combined with fully documented parameters and safety annotations, an agent has everything needed to call this correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so a baseline of 3 applies, but the description earns more: it specifies the alternate return shape { post_id, key, value } when `key` is set, and clarifies that `post_type` is a REST base (default `posts`) with a slug also accepted. That is real meaning beyond the schema text.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Opens with a specific verb+resource ("Gets REST-API-visible meta fields for a post") and immediately bounds the scope to fields registered with show_in_rest. That boundary plus the post_id/key framing makes it distinguishable from wp_get_post and wp_get_term_meta, though no sibling is named explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description tells the agent precisely when to supply `key` (single key, structured return) versus omit it (all meta), and when to use `post_type` (pages/custom post types rather than posts). It never names an alternative tool or states when not to use this one, so the routing guidance is implied rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.